1. Field of the Invention
This invention relates to imaging instruments such as single lens reflex cameras and video cameras having interchangeable objectives or other accessories releasably attached thereto with interconnections for electrical signals therebetween, and more particularly to a device for detecting a failure to establish conductivity between contact at the interconnections, so as to provide assurance that the electrical signals are transferred reliably.
2. Description of the Prior Art
Bayonet devices and screw mounts are often used for coupling cameras and interchangeable lenses. These coupling arrangements do not always insure that when the interchangeable lens and the camera body are in lock with each other, the exposure control signals are transferred between the camera body and the lens with sufficient fidelity to produce proper photographs.
The manner in which these coupling arrangements operate are generally such that the interchangeable lens is first lined up with the camera body, then inserted into the mount of the camera, and then turned about the optical axis relative to the camera over a predetermined angle. If the aforesaid angle is not reached, the complete camera will not perform an accurate and reliable exposure control operation.
A number of safety devices have been proposed to lock the coupling arrangement of the interchangeable lens with that of the camera in the right position. This includes, for example, U.S. Pat. Nos. 4,092,656 and 4,130,358.
In recent years, techniques of electrically controlling the operation of the diaphragm device in the interchangeable lens with a stepping motor or other electromagnetic drive means, and of automatically adjusting the position of the focusing lens member in accordance with the output of the range finding means with the use of an electric motor, have been and are being developed. Cameras and interchangeable lenses employing such techniques are, therefore, required to have electrical signal transmitting channels at or near the coupling arrangements thereof.
In a camera and/or interchangeable lens provided with an electrical signal transmitting channel in the form of a pair of interconnection terminals it will happen that even when an optical or mechanical coupling between the camera and interchangeable lens is made secure, the interconnection terminals fail to make good electrical contact. If so, that is, a sufficient conductivity between the signal terminals of the camera and interchangeable lens is not established, the camera with the interchangeable lens attached thereto will not operate normally.